Dispersal of flammable materials

ABSTRACT

A method and apparatus for dispersal of flammable vapour, for example naphtha, consists of a firewall to restrain the horizontal advance of the vapour and a turbulent steam jet system positioned adjacent to the firewall to entrain the vapour together with air.

United States Patent 1191 Dec. 11, 1973 Cude et al.

[ DISPERSAL OF FLAMMABLE MATERIALS [75] Inventors: Arthur Leslie Cude; Henry George Simpson, Stockton-on-Tees, England [73] Assignee: Imperial Chemical Industries Limited, Millbank, London, England [22] Filed: May 21, 1971 [21] Appl. No.: 145,714

[30] Foreign Application Priority Data May 27, 1970 Great Britain 25,528/70 [52] US. Cl. 169/2 R, 239/209 [51] Int. Cl. A62c 3/00 [58] Field of Search 239/2 R, 14, 566,

239/567, 208, 202, 289, 133, I34, I35, 200, 201; 169/2 R, l, l9, 16

[56] References Cited UNITED STATES PATENTS 3,050,134 8/1962 Multin 239/209 2,751,915 6/1956 RObBl'iS 239/135 1,508,028 9 1924 Robinson 239/289 3,520,345 7/1970 Lillibridge et al 169/2 R 2,337,710 12/1934 Cowan 169/2 R 3,464,172 9/1969 McGee, Jr. 239/209 15,647 9/1856 Driggs 239/200 549,587 11/1895 Schultze... 239/200 802,772 10 1905 McCoy 239/202 Primary Examiner-Lloyd L. King Attorney-Cushman, Darby & Cushman [57] ABSTRACT A method and apparatus for dispersal of flammable vapour, for example naphtha, consists of a firewall to restrain the horizontal advance of the vapour and a turbulent steam jet system positioned adjacent to the firewall to entrain the vapour together with air.

2 Claims, 1 Drawing Figure DISPERSAL OF FLAMMABLE MATERIALS The present invention relates to a method and apparatus for the safe dispersal of potentially dangerous concentrations of flammable vapours which are heavier than air.

In the processing, handling or storage of flammable fluids it is clearly desirable to prevent accidental release of the fluid into the atmosphere. Equipment which is to contain the flammable material is designed specially to prevent such accidental release and opera tion of the equipment is also laid down with this object in view. However, on occasion leakage and spillage of flammable material may occur despite the precautions taken to prevent the accidental release. When release occurs a cloud of heavy vapour may be formed which is capable of travelling considerable distances over the ground in flammable concentrations and which may be ignited by a source of ignition some hundreds of feet from the point of release. This hazard is most apparent in the case of liquefied gases, but it applies equally well to materials which are liquid under ambient conditions, when they are processed or handled at elevated temperatures.

The invention is particularly applicable to flammable fluids which are processed, handled or stored at a temperature above their atmospheric boiling point. In designing plant for these purposes it is the aim to arrange the plant equipment so that there is a sufficient distance between potential sources of leakage or spillage and fixed sources of ignition to allow any escape of flammable vapour to disperse safely before the cloud of vapour reaches a source of ignition.

Nevertheless there are circumstances in which a particular plant area may contain a relatively large number of potential sources of leakage or spillage,.or in which the provision of an adequate safe distance between the source of a leakage or spillage and a source of ignition is impracticable. The chances of a fire and explosion resulting from an accidental release of fluid may then be unacceptably high. We have now devised a method and equipment for the safe dispersal of concentrations of flammable, heavier than air vapours in suchcircumstances.

Accordingly, the present invention is a method for dispersing flammable, heavier than air vapour which comprises restraining the horizontal advance of the vapour and, by means of turbulent steam jets, entraining the vapour together with sufficient air to reduce the concentration of vapour below its lower flammability limit.

Flammable vapours which can be dispersed by the method of the present invention include gases, for example ethylene, and the vapours of liquefied gases, for example liquefied petroleum gas (LPG), and of liquids, for example petrol.

Although the method will disperse a moving cloud of vapour which has a narrow front, it is preferred to promote spreading of the cloud to a wide front, for example while restraining the horizontal advance of the vapour, since the entrainment together with air in the steam jets is then made easier.

The present invention also comprises equipment for dispersing a cloud of flammable vapour which comprises a solid barrier at ground level and a steam jet system associated with the solid barrier to disperse the vapour cloud by entrainment of the vapour with air.

The solid barrier is preferably a firewall which may be made of solid brick but which may also be made of other materials which allow easy building and dismantling of the wall, for example, precast concrete panels and ribbed aluminium sheeting panels. Conveniently the wall is vertical but it may also be inclined away from the vertical, for example, a bund wall, provided that it retards advance of the vapour.

Spacing of the solid barrier from the potential source of leakage or spillage may be governed by the proximity of sources of ignition but if possible, it is desirable to allow the cloud of vapour to broaden its front before meeting the wall. Where circumstances allow, a suitable spacing of the solid barrier from the potential source of leakage or spillage is 9 to 14 metres, preferably ll to 13 metres. This spacing in particular is suitable where ethylene is the vapour to be dispersed.

The steam jet system is preferably a pipe, or pipes, perforated with substantially circular holes and supplied with steam under pressure.

The perforated pipe, or pipes, may be positioned on top of the solid barrier or, relative to the source of leakage or spillage, behind or in front of the solid barrier provided always that the relative positioning of solid barrier and the pipe allows substantially no vapour to evade the steam jet system. A preferred arrangement is to position the pipe level with and adjacent to the top of a vertical wall. The pipe may rest on top of the solid barrier or may be level with or below the level of the top of the barrier.

The length of the perforated pipe is preferably at least as great as the distance between the potential source of escape and the solid barrier on which it is placed. Preferably the pipe is long enough to surround the potential source of escape.

Preferably the jets in the perforated pipe are directed upwards so that in operation, vapour reaching the solid barrier and steam jet system is entrained in the jets of steam together with a much larger quantity of air. It is preferred for the steam to issue at at least sonic velocity from the holes in the perforated pipe or pipes.

To allay spark discharge of static electricity generated by the steam passing through the holes in the perforated pipe it is desirable to ensure that the steelwork of the steam jet system and all other steelwork and electrically conducting material in the vicinity of the steam jets is earthed.

Conveniently, vapour detectors are provided between the potential source of leakage or spillage and the solid barrier to detect and give warning of the presence of flammable vapour. Preferably, the detectors also provide an audible and/or visible signal which, optionally, actuates the steam jet system so that dispersal of the vapour commences as soon as possible after its presence is detected.

One embodiment of the invention will now be described with reference to the accompanying drawing which is a diagrammatic view in perspective.

The equipment comprises a wall 1 made of precast concrete panels and 1.5 metre high, spaced about 12 between the plant 2 and the wall 1 to detect and give warning of the presence of flammable vapour.

A vapour escape of ethylene at a rate of 7.2 kg/s. was found to require a distance of 88 metres from the escape point for safe dispersal using natural air movement at a wind speed of 2.2 metres/second.

A similar escape in the same air conditions was safely dispersed in 28 metres from the escape point using the wall and steam curtain hereinbefore described. The initial velocity of the steam jets was of the order of 425 metres/second and the height of the steam curtain formed was 24 metres.

We claim:

from petrol. 

2. A method according to claim 1 wherein the flammable, heavier-than-air vapour comprises ethylene, the vapours of liquidified petroleum gas or the vapours from petrol. 